1. Field of the Invention
The present invention relates to a magnetic annealing tool heat exchange system which reduces the manufacturing cycle for the workpieces processed therein. The system provides an efficient heating and cooling cycle, as well as flexibility, as various components of the system can be independently controlled, depending on the process performed.
2. Description of Related Art
Magnetic annealing is one of three processes that are required to manufacture a Magneto Resistive Random Access Memory (MRAM) chip on a standard Complementary Metal Oxide Semiconductor (CMOS). To successfully anneal an MRAM wafer, the ferromagnetic layer must be held at a predetermined temperature in a magnetic field for a period of time long enough for the crystals to orient themselves in a common direction upon cooling. The process, which is also referred to as “soak” is carried out in an inert, reducing or vacuum environment to prevent oxidation of wafers, while they are held at the predetermined temperature.
Magnetic annealing tools generally operate batch-wise and perform a number of steps. They include heating, soaking and cooling steps which are carried out in a magnetic field, typically between 0.02 and 7.0 Tesla. The cost of MRAM chip manufacturing is linked to the magnetic annealing tools, where the productivity (acceptable devices produced per hour) is the product of density (number of devices per wafer), throughput (wafers per hour) and yield (ratio of acceptable devices to total number of devices processed) as dictated by the overall thermal/anneal cycle.
Several magnetic annealing systems have been proposed in the related art. Some of the systems either reduce the heating time or the cooling time associated with the magnetic annealing process. However, these process heating and cooling steps are in direct conflict with one another and, therefore deleteriously affect the annealing cycle. For example, U.S. Pat. No. 6,303,908 to Yamaga et al discloses a heat treatment apparatus which performs a heat treatment in a magnetic field. The apparatus has a heater which is arranged between a vacuum vessel and a magnetic field generator. The electric heater is arranged so as to surround the outer peripheral surface of the vacuum vessel, and a fluid cooling section is arranged between the electric heater and the magnetic field generator.
U.S. Pat. No. 6,741,804 B2 to Mack et al concerns the processing of electronic device, and methods for rapidly heating substrates. In particular, this patent document discloses a cylindrical lamp array structure surrounding a cylindrical process tube. The lamps are positioned with respect to the cylindrical process tube so that the sides of the lamps focus light energy in the direction of the lengthwise central axis. The substrates in the cylindrical process tube have a lengthwise central axis. The substrates are oriented within the cylindrical process tube so that the major surfaces of the substrates are substantially normal to the lengthwise central axis.
U.S. Pat. No. 6,769,908 B2 to Kawase relates to a wafer heat-treatment system, and more particularly to a lamp-heating single-wafer processing heat-treatment method that processes a single wafer by a film forming process. This patent document discloses an apparatus having a hollow space between the heaters and the wafer. During heating the hollow space is evacuated, thereby preventing heat transfer by conduction across the wafer chamber to the exterior. During cooling the hollow space is rapidly filled with gas, causing a drop in temperature and subsequent cooling.
U.S. Patent Application Publication No. 2004/0218913 A1 to Melgaard is directed to an annealing oven for magnetic and non-magnetic heat processing of work pieces, and to heat transfer techniques. The oven includes a shell into which a removable rack is placed. The rack has at least one plate which may be heated or cooled by a plate fluid conduit in contact with the plate and through which a heating or cooling fluid can be passed. The workpieces therein are primarily heated and cooled by conductive and radiant heat transfer.
Some of the disadvantages associated with the related art systems is that they are not sufficiently flexible to control and vary the heating and cooling steps independently and efficiently.
To overcome the disadvantages of the related art, it is an object of the present invention to shorten the thermal exchange cycle of the magnetic anneal tool by efficient heating and rapid cooling of the process chamber disposed in the magnetic anneal tool.
It is another object of the present invention to provide a separate and independent control of the process parameters affecting the process chamber of the magnetic anneal tool.
It is a further object of the invention to provide a system and process with independent control of the flow rate, temperature, pressure and composition of the gas supplied to the element chamber of the magnetic anneal tool.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification, the drawings and claims appended hereto.